Hydrostatic drives have found extensive use in providing motive power in tracked vehicles such as crawler tractors, excavators, and military tanks. Wheeled vehicles such as road rollers, agricultural combines, and others also use hydrostatic drives.
Dual range or two-speed hydrostatic drives are often desirable in such equipment. Throughout a low range, relatively low vehicle speed but high drive torque is provided for travel over difficult terrain. In a high range, relatively high vehicle speed and lower drive torque is provided.
Many of these previously offered hydrostatic drive devices use relatively large and expensive hydraulic pumps and motors to provide the motive power for the vehicle. To provide the desired dual range feature, it has often been necessary to provide costly, complex shifting mechanisms, two-speed drop boxes, and other apparatus.
It is accordingly a general object of the present invention to provide a dual-speed hydrostatic drive which is rugged, yet which requires but few major elements.
More specifically, it is an object to provide a hydrostatic drive which uses relatively small and inexpensive hydraulic pumps and motors.
Conversely, it is an object to provide a hydrostatic drive which provides increased theoretical start-up torque and increased maximum speed without requiring larger hydraulic pumps and motors.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.